We have various forms with required fields.  Some are lookup fields and others are not.  However on a few lookup fields for example, when the form is launched it immediatly seems to warn about putting in an option.  As if the user has clicked in it but not selected anything.  For example:

Is a lookup dropdown menu.  This is what it looks like when the form is launched.

However on another form we have this field.  It is not the first field in the form just like Document Type.  When the form is launched it shows like this:

We have other lookup fields on forms and some of them do this and others do not.  Is there a reason why some of them immediatly throw this "error" while other lookup lists do not?

Thanks